I. Field of the Invention
The present invention relates to radio communications. More particularly, the present invention relates to a private code division multiple access (CDMA) wireless communications system as well as CDMA Tiered Service capability.
II. Description of the Related Art
Multiple access modulation techniques are efficient techniques for utilizing the limited radio frequency spectrum. Examples of such techniques include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA).
CDMA modulation employs a spread spectrum technique for the transmission of information. A spread spectrum system uses a modulation technique that spreads the transmitted signal over a wide frequency band. This frequency band is typically substantially wider than the minimum bandwidth required to transmit the signal.
A form of frequency diversity is obtained by spreading the transmitted signal over a wide frequency range. Since only part of a signal is typically affected by a frequency selective fade, the remaining spectrum of the transmitted signal is unaffected. A receiver that receives the spread spectrum signal, therefore, is affected less by the fade condition than a receiver using other types of signals.
The spread spectrum technique is accomplished by modulating each base band data signal to be transmitted with a unique wide band spreading code. Using this technique, a signal having a bandwidth of only a few kilohertz can be spread over a bandwidth of more than a megahertz. Typical examples of spread spectrum techniques are found in M. K. Simon, Spread Spectrum Communications, Volume I, pp. 262-358.
In a CDMA-type wireless communication system, multiple signals are transmitted simultaneously at the same frequency. A particular receiver then determines which signal is intended for that receiver by a unique spreading code in each signal. The signals at that frequency, without the particular spreading code intended for that particular receiver, appear to be noise to that receiver and are ignored.
The present CDMA air interface, however, is not well suited to private systems. A private system that uses the public CDMA carrier is required to provide soft hand-off support to public users in its coverage area to avoid RF interference issues. The reason is that when a radiotelephone, operating on the macro public system, moves closer to the private micro-cell, it creates interference to the micro-cell users. It is thus imperative for the private micro-cell to be able to control the power of that radiotelephone (i.e. support of hand-off); otherwise, interference becomes so strong that it makes the private micro-cell inoperative.
In a single carrier deployment, therefore, RF interference limits the feasibility of private home and office CDMA systems. There is a resulting unforeseen need for a private wireless communication system using a CDMA air interface. As a result it is almost impossible for CDMA systems to support private systems on the same RF carrier frequency as the overlaying public system. Furthermore, service providers cannot have geographic granularity of billing and other services for a region that is smaller than a natural CDMA cell or sector. There is accordingly a need for a new scheme to provide the capability of a private/residential system services, as well as tiered services in CDMA wireless communication systems.
The present invention encompasses a private/residential wireless communication system that uses a code division multiple access air interface. The private system is overlaid by a public CDMA system. The public CDMA system comprises an antenna coupled to a base station. The private system may operate on a predetermined frequency, or it may share the same radio resources with the overlaying public system. The private system may be assigned a predetermined identification (for example User Zone identification UZID). When the private system operates on a different frequency than the overlaying public system, the private system may be assigned one (or more) predetermined User Zone(s) identification.
In certain embodiments, the public base station broadcasts the predetermined identification over a channel for reception by a radiotelephone. This instructs the radiotelephone as to what private systems are being served by the public system.
In alternate embodiments, the public system also broadcasts frequency, band class, pseudorandom noise offset information, and geographical location information regarding the private systems that are served by the public system. If the radiotelephone has the ability to determine its geographic location, it can find the private systems by using the broadcast geographic information.
In alternate embodiments, the private system is autonomous to the public system and no information regarding the private system is broadcast by the public system.